Field of the Invention
The present invention relates to a surface light source device and a display device using the surface light source device.
Description of the Background Art
A display device in which a display panel itself does not emit light, such as a liquid crystal display device, generally includes a surface light source device for irradiating the display panel with light. In a related-art display device, even when a dark image is displayed, light similar to that used when a bright image is displayed is emitted from the surface light source device. In recent years, however, a technology called “local dimming” has been put into practice, where a screen of a display device is divided into a plurality of sections (cells) and brightness of the surface light source device is adjusted partly in accordance with the brightness of an image to be displayed in each cell. According to the local dimming technology, excessive light emission of the surface light source device is suppressed, and hence power consumption of a display device can be reduced.
Japanese Patent Application Laid-Open No. 2011-023331 discloses a surface light source device having a configuration in which a light guide plate is divided into a plurality of cells (light guide blocks) by grooves formed in the light guide plate, and light sources are accommodated in the grooves. Further, Japanese Patent Application Laid-Open No. 2008-27886 discloses a configuration of arranging, in each region partitioned by a lattice-shaped partition wall, a planar illumination light source device including light sources, a light guiding body, and reflecting means.
In Japanese Patent Application Laid-Open No. 2011-023331, a dot pattern or a prism pattern is formed in a surface of the light guide plate to enhance straightness of light entering each cell and prevent light emission from each cell to cells adjacent thereto, thereby suppressing generation of unevenness at a boundary portion of each cell such as a bright line and a dark line. Therefore, the light sources inevitably need to be controlled in each of the cells. Further, Japanese Patent Application Laid-Open No. 2008-27886 has an object to make emission light of a surface light source device disposed in each cell uniform, thus not being intended to prevent unevenness of luminance at a boundary portion of cells.